Insights into interfacial speciation and deposition morphology evolution at Mg-electrolyte interfaces under practical conditions

Rechargeable magnesium(Mg)battery technologies show the promise of low cost,less safety concerns and relatively higher energy density.Interrogating the critical issues on the Mg stripping/plating performance as well as the Mg metal anode-electrolyte interfacial chemistry is one great importance under the practical areal capacity and rate conditions.In this work,we systematically investigate the electrochemistry of Mg stripping/plating processes within four distinctive Mg-ion electrolytes and the Mg anodeelectrolyte interfacial chemistry under practical conditions.Electrochemical results show that the cycle life of Mg//Cu asymmetric cells using these above electrolytes is significantly shortened(less than 10 cycles)when tested at a practical areal capacity of 10 mAh cm^-2.Further optical and electron microscopic analyses reveal that the gradual growth of the Mg deposits is susceptible to detachment from the copper substrate,where the initial nucleation process might occur.In spite of showing an interconnected particle-like morphology,the Mg deposits could easily penetrate the porous separator,leading to cell failure.The co-deposition of metallic Al is revealed from surface region to bulk,while the Cl-containing species exist in the near surface of Mg deposits.Our work not only highlights the critical impacts of areal capacity on the performances of Mg stripping/plating process,but calls for further efforts to eliminating the safety concerns of Mg anode under practical conditions.